Disable Classic block: Always register, hide from inserter conditionally

[yuliyan]

What?

Always register the core/freeform (Classic) block. Its inserter availability is now controlled by supports.inserter instead of conditionally skipping registration.

Why?

Trying a different approach for the experiment - instead of skipping registration, we always register the block but hide it from the inserter. This preserves support for existing posts that already contain a Classic block, while preventing new ones from being added.

The exact condition for hiding the block in the inserter will be tweaked in follow-up PRs.

How?

The Classic block is now always included in the list of registered core blocks. When the experiment is enabled, its visibility in the inserter is controlled via supports.inserter based on the window.wp.needsClassicBlock flag.

Testing Instructions

1. Open a post that does not contain a classic block.
2. Confirm the Classic block is not in the inserter when the "Disable Classic block" experiment is enabled.
3. Disable the experiment and confirm the Classic block appears in the inserter.
4. Open a post that contains a classic block and confirm it still renders/edits correctly in both cases.

Testing Instructions for Keyboard

Screenshots or screencast

N/A

Use of AI Tools

Opus 4.7

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: yuliyan <yuliyan@git.wordpress.org>
Co-authored-by: tyxla <tyxla@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[tyxla]

Works as expected, thanks 👍